Report investigates dual and triple co-located signage

When driving on a motorway, up-to-date information on the speed limit, traffic delays or even an alternate route to get home quicker is important in making the journey as safe as possible.

But, can all this information be too much for a driver to handle on heavily trafficked routes such as motorways?

“Motorways, particularly in the city area, are where a driver can need a lot of information at the same time and has to be well-prepared to deal with it,” says Peter Cairney, ARRB National Technical Leader Behavioural Science. Dr. Cairney explains that direction signs (DS), variable message signs (VMS), and variable speed limits/lane control signs (VSL/LCS) each contribute to the safety and effectiveness of these busy roads.

VMS, for instance, give information on different directions or alternate routes off the motorway should an accident occur. Likewise, VSL/LCS, can update drivers with vital information on lane speeds. Dr. Cairney says that these signs need to be seen well before they have to be acted on. This gives drivers time to comprehend the information and plan the action to be taken.

On motorways, these signs are displayed on overhead gantries. When the situation requires it, two different types of signs are displayed alongside one another on the same gantry. However, there are some situations, particularly in inner-city areas, where it would be convenient to place three different signs on the same gantry. The question is, does this triple co-location result in too much information for the driver to absorb in the time available, particularly when they may be coping with a demanding traffic situation?

The triple co-location of DS, VMS and VSL/LCS on motorways has been used widely in Europe, says Dr. Cairney. Australia has co-located signs on some of its motorways, but Australian practice does not yet extend to triple co-location.

Dr. Cairney and Dr. Clarissa Han from ARRB prepared the report, Ability to Absorb Information Through Electronic and Static Signs, which was released in May. The report consists of a literature review and a driving simulator study.

The literature review examined current practices across a range of countries and the research evidence on the co-location of DS, VMS and VSL/LCS. The aim of the simulator study was to investigate how well drivers could absorb the information from co-located signs, and if there was a difference between dual co-located signs and triple co-located signs.

The human factor was the major variable put to the test in the research stage.

Researchers at the Centre for Accident Research & Road Safety at the Queensland Institute of Technology (CARRS-Q) conducted the study using CARRS-Q’s advanced driving simulator (ADS) study. The work looked at the impact of increased sign complexity on two higher-risk road user groups, older (65 years old or more) and younger (18 to 22 years old) drivers. The ADS physically put participants in the driver’s seat. Participants steered the vehicle and made the decisions drivers would normally make.

Dr. Cairney explains that individuals taking part in the trial were subjected to a range of driving scenarios in the simulator. Each scenario ran for around 10 to 15 minutes, and some involved a simulated emergency where the car in front of the participant’s vehicle brakes abruptly as it approached a co-located sign. Both double and triple co-located signs were present in the simulation.

The test was to ascertain whether or not drivers could take in and respond to the information on the signs while coping with unpredictable situations on the road. Neither dual nor triple co-location appeared to affect the driver behaviour during standard driving, speed limit change. and lane closure situations.

Dr. Cairney says drivers coped well with emergency situations, Participants were able to select the correct destination whether signs were co-located or not, although they did not always capture all the information from the co-located signs, he says. Few aspects of the driving task were more adversely affected by triple co-location than by dual co-location, he adds. More drivers exceeded the speed limit at “check points” on the simulated driving route, but overall speeds were no higher, suggesting the differences in speed for dual and triple co-location signs were small. He says that generally, drivers responded well to the simulated emergency, although there the study suggested that some responses may have been slower with the triple-co-location signs.

Dr. Cairney says the pros definitely outweigh the cons when it comes to implementing the co-location of these three signs on Australian motorways.

“I think [the study results] gives us the confidence to go ahead and look at using triple co-located signs where they are needed,” he says.

Dr. Cairney says triple co-located signs are going to be important for the immediate future of Australian roads. There are a few busy motorways around major cities which would be suitable. Triple co-location arrangements of DS, VMS and VSL/LCS can update road users on travel times, delays and even ease the flow of traffic on these road networks.

“There’s very much a potential application to help deal with congestion, particularly when there’s a crash or other problem with the system,” he says.

The report concludes that the dual co-location of VSL/LCS, VMS and/or DS is a practical arrangement for the country’s motorways, but should be treated with caution, and considered only where other arrangements are impractical. Further evaluations of triple co-location in a real-life setting are called for.

The report recommends that dual co-location guidelines be considered for Austroads’ next revision of the Guide to Traffic Management (part 10), and that the relevant standards be updated in the Australian Standard Manual of Uniform Traffic Control Devices to reflect this.

While triple co-location can improve the effectiveness of motorway signing, Dr. Cairney suggests the way absorb information on our roads may change in the future. New technology is enabling drivers to receive this kind of information directly, via their vehicle’s on-board computer. “That is something that is likely to be important in the future, but roadside VMS are likely to be important for the next generation or so.”